The present invention relates generally to the data processing field, and more particularly, relates to a method and apparatus for preemptive head crash avoidance in a direct access storage device (DASD).
Computers often include auxiliary memory storage units having media on which data can be written and from which data can be read for later use. Disk drive units incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks.
Data located on a particular track on a disk surface is read or written by properly positioning a data transducer head directly over the track. In order to maintain the head in proper position over the data track, track-following servo systems often are incorporated into disk drives. Servo position control is used to position the data heads in registration with the data information tracks. A sector servo system uses the data heads as servo transducers in a time multiplexed fashion. As a head is following a particular track on a rotating disk, the head will pick up data information and servo information alternately. Servo information, interlaced with data information, is prewritten on the disk surfaces at manufacturing time within narrow radial sectors as spokes on a wagon wheel. A servo system that interlaces data and servo information is commonly referred to as sector servo or embedded servo. Another servo system uses a dedicated servo transducer head to read position signals recorded in servo information tracks on a dedicated disk surface. The data heads are ganged with the servo head for simultaneous movement relative to the data information tracks and the servo information tracks. To access the disk drive unit, a feedback sector servo controlled drive system locates the head in a desired position, where data is to be written or read.
A head crash often renders a conventional disk drive inoperable. One of the reasons for magnetic recording heads crashing of a disk surface, for example, causing catastrophic failure is the presence of protruding disk defects or asperities. The manufacturing glide test screens disk drives for unacceptable disk asperities in order to reduce the probability of a crash. Some of the disk defects also, are grown during the life of the drive. These defects include ding marks, pits, gouges, protruding disk defects or thermal asperities. Large surface bumps are notorious for causing physical head-to-disk contact, which is the precursor for a fatal disk crash. All users of hard disk drives dread even the thought of a fatal disk crash, since all data stored on that unfortunate disk drive may be lost forever.
A need exists for a method and apparatus for preemptive head crash avoidance in a direct access storage device (DASD).
A principal object of the present invention is to provide a method and apparatus for preemptive head crash avoidance in a direct access storage device (DASD). Other important objects of the present invention are to provide such method and apparatus for preemptive head crash avoidance in a direct access storage device (DASD) substantially without negative effect; and that overcome many of the disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for preemptive head crash avoidance in a direct access storage device (DASD). At least two actuators are provided in the DASD. Each actuator services at least one transducer head. Monitoring for a predicted head crash is performed. Responsive to an identified predicted head crash, a transducer head for the predicted head crash is unloaded and unloading each additional transducer head being serviced by an actuator for the transducer head for the predicted head crash.
In accordance with features of the invention, a data backup process is performed. Responsive to an identified predicted head crash, data are transferred from a disk surface associated with the transducer head for the predicted head crash and transferring data from each disk surface associated with each additional transducer head being serviced by the actuator for the transducer head for the predicted head crash.